In at least a substantial portion of the United States, machines for washing beverage glasses are required to meet standards set by the National Sanitation Foundation (NSF), according to which such a machine must subject glasses to a thorough soil-removing wash with a detergent solution that is at a temperature of at least 120.degree. F., and then to a thorough rinse with a germicidal solution. Meeting these standards with an optimally efficient machine imposes significant costs for water, chemicals and electric current; but prior glass washing machines capable of meeting NSF standards, far from being efficient, have tended to operate in a very wasteful manner.
In a glass washing machine with a rotary carrier, glasses are carried around a circular path, one portion of which is in an access zone and the remainder of which is in a cleansing zone. Dirty glasses are loaded onto the portion of the carrier that is in the access zone. The rest of the carrier is meanwhile blocked by the spray nozzles and spray shields in the cleansing zone and is thus inaccessible for loading and unloading. When the machine is operating, liquid is normally discharged from all of the nozzles in the cleansing zone, and a certain amount of waste is involved in discharging such liquid against empty portions of the carrier.
An early rotary carrier machine intended specifically for washing glasses is disclosed in U.S. Pat. No. 2,360,156 to Ohme et al, issued in 1944. In that machine only hot water was discharged from the nozzles in the cleansing zone. On its way to the nozzles, the water passed through a water power motor by which the carrier was driven. Obviously, this machine was intended to operate continuously, rather than being manually turned on and turned off at intervals, and therefore it was likely to be left running with no glasses in it that needed cleaning, thus wasting water and the energy needed to heat it. The patent evidences a realization that letting the machine run unnecessarily was more convenient than operating it for economy, saying: "If desired, vessels may be allowed to repeatedly travel through the machine and subsequently removed when desired for use." This machine had n provision for the addition of detergent and germicide chemicals, so that it would not have complied with present NSF standards; but with such provisions its cost of operation would have been further increased by wastage of those chemicals.
A relatively recent machine specifically intended for washing glassware is disclosed in U.S. Pat. No. 3,878,856 to Hall, issued in 1975. It, too, had to be manually stopped as well as manually started, and therefore it could operate wastefully until someone remembered to shut it off and had the opportunity to do so. The likelihood of such manual shutoff has been measured by actual tests in a busy tavern-restaurant, using a metering device on a manually controllable glass washer. The tests showed that the machine was consistently allowed to run continuously for about eight hours at a time but was actually washing glasses during only about two hours of that period.
Other rotary carrier machines that operate continuously unless manually turned off are disclosed in U.S. Pat. Nos. 1,681,839 to Breton, 1,762,847 to Webb and 2,558,816 to Campbell. The last-mentioned patent discloses a milk can washer wherein the rotary carrier has a defined position for each can to be carried and has a lever at each position which is tripped by loading a milk can onto that position and which cooperates with valves that control flow of cleaning liquids to nozzles in respective sectors of the cleansing zone, so that no liquids are discharged against unoccupied portions of the carrier. This arrangement is obviously not suitable for a beverage glass washer that must accommodate glasses of widely varying shapes and sizes.
U.S. Pat. No. 3,731,696, to Hackney, discloses a rotary carrier glass washer having two auxiliary disc-like platforms that rotate in frictional engagement with the carrier, onto one of which dirty glasses are loaded and onto the other of which clean glasses are delivered by the carrier. In the specifically disclosed embodiment, the machine, once started, operates continuously, but the patent mentions that an automatic on-off switch may be so positioned relative to the unloading platform "that any object touching a contact lever of the switch will turn the apparatus off". This does not, in itself, solve the problem of wasteful operation because removal of all glasses from the unloading platform can leave the machine running with an empty carrier.
In machines disclosed in U.S. Pat. Nos. 2,703,580 to Cole, 3,094,997 to Nolte et al and 3,306,580 to Pahl et al, the rotary carrier moves intermittently to carry articles on it stepwise from an access zone, through each of a succession of cleansing zone sectors and back to the access zone, with a period of dwell for each sector of the cleansing zone. The machine of Pahl is used for cleaning insulators in an industrial process and is designed to be constantly attended by an operator who loads and unloads it. In the utensil washing machine of Nolte et al the carrier is rotated manually, requiring substantially constant presence of an attendant during its operation and thus exchanging the possible cost of wasted water, chemicals and current for probably higher labor costs. In the glassware washing machine of Cole the rotary carrier is likewise rotated manually for each advance, but a timer mechanism stops discharge of cleansing liquids after the carrier has remained in any one of its positions of rotation for a predetermined time interval so that "the operator is free to leave the machine when desired".
A very important disadvantage of moving the rotary carrier intermittently and stepwise is that glasses are stationary relative to the spray nozzles all during their period of dwell in each sector of the cleansing zone. Because tavern beverage glasses are usually of different shapes and sizes, they necessarily have a random arrangement on the carrier so that some of them can partly shield others from direct impingement by sprayed liquid. Such shielding can occur only transiently when the glasses move at a steady rate through the cleansing zone, since every glass is then presented in a variety of orientations to the spray from each nozzle in every sector of that zone. To avoid this shielding problem, the above mentioned Nolte et al patent teaches that the nozzles should be mounted on rotating arms, but this solution tends to impose limits upon the area that can be covered by spray from the orbitally moving nozzles, as well as being obviously expensive and potentially troublesome.
In addition to providing for total sanitation of glasses with optimum cost effectiveness and maximum convenience for the personnel who work with it, a completely satisfactory glass washing machine must have a high rate of throughput combined with utmost compactness. A busy tavern cannot have enough glasses on hand to operate through a full business day without washing a substantial number of them, and when clean glasses are needed they should be available without undue delay for a slow washing cycle. On the other hand a tavern glass washer is ordinarily located behind the bar, where space is limited, and therefore high capacity cannot be gained at the expense of utmost compactness. Another consideration in this respect is that the machine must be capable of being so positioned in relation to a bar that a bartender can load it and unload it without turning away from customers at the other side of the bar, and must be so arranged that no part of it interferes with the bartender's full view of customers or with access to all parts of the bar top.
Although some prior glass washing machines have been capable of achieving totally sanitized glasses at a reasonable rate of throughput, and have been reasonably compact, none has met the additional important requirements for operation with minimal waste of water, chemicals and electric current and for requiring minimum attention from bar and table service personnel for the attainment of such economy. Evidently the simultaneous satisfaction of all of these essential requirements has heretofore been well beyond the reach of mere skill in the art.